1. Field of the Invention
The present invention relates to a communication apparatus to which a plurality of public lines are connected and which is capable of transmitting/receiving signals by switching the lines.
2. Description of the Related Art
Hitherto, only one public line has been stored in a facsimile machine. Because the public line is occupied when either one of operations of transmitting image signals from one facsimile machine to a destination facsimile machine, or receiving image signals transmitted from an originating facsimile machine, it has been difficult to perform either one of the operations when performing the other operation. Accordingly, a facsimile machine other than the destination or originating facsimile machine cannot transmit image signals to the one facsimile machine during when it transmits/receives image signals. Therefore, transmission waiting time of the other facsimile machine has been prolonged in the case described above.
To overcome the above, technologies for storing a plurality of public lines in one facsimile machine have been developed in order to receive/transmit image signals in parallel by a single facsimile machine. As prior art technologies of this sort, there have been facsimile machines disclosed in Japanese Unexamined Patent Publications JP-A 4-23673(1992) and 5-219275(1993). The facsimile machine in JP-A 4-23673 transmits the same image signals to a plurality of facsimile machines by means of the so-called multi-address calling. At this time, the operation for transmitting to each destination is initiated by shifting transmission times, by a predetermined time, in order to prevent all lines that are stored in the facsimile machine from being used at the same time for the transmission of the image signals. The facsimile machine disclosed in JP-A 5-219275 (1993) portions out the stored plurality of lines into lines to be used for transmission and lines for receiving corresponding to a factor of use of the lines. Although the facsimile machine storing the plurality of public lines has been thus arranged so that all of the stored lines are not used at the same time, all of the lines are still used at the same time when an unspecified number of calls to be received are concentrated in all of the lines. This causes a transmission waiting state.